hdu 5879 Cure 2016ACM/ICPC青岛赛区网络赛1002

Problem Description

Given an integer  n , we only want to know the sum of  1/k2  where  k  from  1  to  n .

 

Input

There are multiple cases.
For each test case, there is a single line, containing a single positive integer  n . 
The input file is at most 1M.

 

Output

The required sum, rounded to the fifth digits after the decimal point.

 

Sample Input

  
  

   
   1
2
4
8
15
  
  

 

Sample Output

  
  

   
   1.00000
1.25000
1.42361
1.52742
1.58044
  
  

小数据暴力一下，k->inf的时候数列之和收敛π^2/6【当时是敲了个暴力然后把1000w以上的直接用1000w输出了】